1. Field of the Invention
The present invention relates to series-resonance-loaded inverters having ground-fault-protection and EMI filtering, particularly as used for powering gas discharge lamps.
2. Description of Prior Art
Ballasts with built-in ground-fault-protection means have been previously described, such as in U.S. Pat. No. 4,563,719 to Nilssen.
Ballasts having built-in EMI filtering means also have been previously described, such as in U.S. Pat. No. 4,684,850 to Stevens.
Ballasts using a series-resonance-loaded output have also been previously described, such as in U.S. Pat. No. 4,370,600 to Zansky.
In an inverter where a gas discharge lamp load is parallel-connected across the tank capacitor of a high-Q LC circuit that is resonantly series-excited by a high-frequency voltage output of the inverter, it is necessary to provide some means to protect against the high currents and voltages resulting due to so-called Q-multiplication whenever the lamp load is removed or otherwise fails to constitute a proper load for the LC circuit.
In U.S. Pat. No. 4,370,600 to Zansky, circuit protection is provided by way of providing to the LC circuit an alternative load in the form of a voltage-clamping means; which voltage-clamping means acts to load the LC circuit during any period when the lamp does not constitute a proper load therefor.
The voltage-clamping is accomplished by rectifying the Q-multiplied voltage output of the LC circuit and by applying the resulting DC output to the inverter's DC power source.
However, during any period when voltage-clamping does occur, a relatively large amount of power circulates within the electronic ballast means: from the inverter's output, through the LC circuit, and back into the inverter's DC power source by way of the voltage-clamping means.